Diversity in the Scutes of Chelonia. 9 



in Macroclemmys) ; (c) paired inframarginals (preserved in sea tur- 

 tles and, as inguinals and axillaries, in most other turtles, but 

 entirely lost in a few land tortoises) ; and finally, (d) unpaired inter- 

 plastrals — preserved normally only as a single intergular in a few 

 species, as Chelodina. In general, the principal rows are retained in 

 all turtles, but the subordinate rows are largely lost. Remnants of 

 these latter series, however, are retained in the normal condition 

 of some species, and, further, reappear as atavistic abnormalities in 

 individuals of species that do not normally possess them. Thus^ 

 inframarginals were found "abnormally" in Graptemys geograpliica 

 and Clirysemys marginata, etc. ; interplastrals, in specimens of 

 Chrysemys, Chelydra, and Graptemys. IsTewmann does not seem to 

 have found either neuro-cosials or siipramarginuls as individual 

 variations. 



Furthermore, ISTewmann believes that the number of scutes of the 

 neural and costal series was formerly about twice as great as at 

 present, and that alternate scutes have been forced out and lost, 

 but that these, again, recur in individuals as atavisms. 



There has been, then, a reduction both in the number of rows and 

 in the number of scutes in a row; but atavistic occurrences of the 

 lost elements are met with in abnormal individuals of many species. 

 From a systematic study of these atavisms, we may infer something 

 of the evolutionary history of the Chelonian carapace and plastron. 



ISTewmann differs from Hay in supposing fourteen original rows 

 as opposed to Hay's twelve; in seeking the ancestral type not in 

 Dermochelys. but in the disposition of the scutes of the base of the 

 tail of Chelydra ; in supposing but a comparatively small number of 

 original scutes in each series of the carapace ; and in seeking a basis 

 for his views in the systematic study of atavisms. 



The question of the value of the anomalous scutes as evidence of 

 phylogeny will be discussed in a later portion of this paper. 



Use of Terms. 



The term "scute" will apply invariably to a horny shield of the epidermal 

 carapace; "plate" to an element of the bony carapace; "seam" refers to the 

 line of separation of adjacent scutes, as "suture" to that of adjacent bones. 



The nomenclature of the scutes will be clear from Text-figs. A, B and C. 



